What causes blurred vision?

Blurred vision is one of the most common reasons people book an eye examination. It can be mild or severe, sudden or gradual, and it can affect one eye or both. Importantly, blurred vision is a symptom, not a diagnosis. Finding the cause is what matters, because the treatment can range from a simple pair of glasses to urgent surgery.

Refractive errors

The most common cause of blurred vision is a focusing problem. Short-sight, long-sight, astigmatism and presbyopia all make images appear blurry because light is not focusing sharply on the retina. This is usually corrected with glasses, contact lenses or laser eye surgery. A gradual change in blur, especially if it comes and goes with tiredness, is often due to a change in prescription.

Dry eye

Dry eye is surprisingly common and can cause fluctuating blur, particularly during computer use, reading or in air-conditioned environments. The tear film is the first surface that light passes through, so if it is unstable, vision becomes smeary or foggy. Lubricating drops, lid care and environmental changes often help.

Cataracts

A cataract causes the natural lens inside the eye to become cloudy. Vision becomes hazy, colours dull, and night driving becomes harder due to glare. Cataracts usually develop slowly and are more common with age, but they can also be caused by medication, trauma or other eye conditions. Surgery is the only definitive treatment, and it is highly effective.

Glaucoma

Glaucoma damages the optic nerve, usually due to raised pressure inside the eye. In its early stages, glaucoma does not cause blur or any noticeable symptoms. It quietly affects peripheral vision first. By the time central vision is blurred, the damage is often advanced. Regular eye examinations are essential, especially if you are over 40 or have a family history of glaucoma.

Age-related macular degeneration

Age-related macular degeneration, or AMD, affects the central part of the retina called the macula. It causes blurred or distorted central vision, making it difficult to read, recognise faces or see fine detail. There are two types: dry AMD, which progresses slowly, and wet AMD, which can cause rapid vision loss and needs urgent treatment.

Diabetic retinopathy

Diabetes can damage the blood vessels at the back of the eye. In the early stages, diabetic retinopathy may cause no symptoms, but as it progresses it can cause blurred, patchy or distorted vision. Good blood sugar control and regular retinal screening are the best ways to protect sight. If diabetic macular oedema develops, treatment with injections or laser may be needed.

Retinal detachment

A detached retina is an eye emergency. Symptoms include a sudden shower of floaters, flashes of light, and a curtain or shadow over part of the vision. Vision can become blurred very quickly. If a retinal detachment is not treated promptly, it can cause permanent blindness. Anyone with these symptoms should seek same-day emergency eye care.

Stroke and neurological causes

Sudden blurred vision, double vision, or loss of part of the visual field can be a sign of a stroke or another neurological problem. If blurred vision is accompanied by weakness, numbness, difficulty speaking or a severe headache, call emergency services immediately. These symptoms are not something to wait and see.

Migraine and other temporary causes

Some people experience blurred vision or zigzag patterns before a migraine headache. This usually lasts 20 to 40 minutes and then resolves. While alarming, it is usually harmless. However, any new or different visual disturbance should be discussed with a doctor, especially if it is the first episode or if it does not go away.

When to seek urgent help

Get urgent same-day eye care if you have:

- Sudden blurred vision in one or both eyes

- New flashes of light or a sudden increase in floaters

- A curtain or shadow over your vision

- Painful red eye with blurred vision

- Blurred vision with headache, nausea or halos around lights

- Blurred vision with neurological symptoms such as weakness or speech difficulty

Next steps

If your vision has changed, do not ignore it. A comprehensive eye examination can identify the cause and guide the right treatment. Even if the blur seems minor, early assessment is the best way to protect your sight and address any underlying condition before it progresses.